Here is a long and considered reflection on items in Smash for people who want some context.
The whole reality of the situation is too complex to fit into a couple short posts, but my take is: Smash as a *product" is sold on the idea of seeing familiar characters in chaotic party-fights that are easy to control, carefully balanced against the fundamentals of fighting games: outguessing your opponents, using attacks to control space on the screen, using good timing to reduce your risks and punish other players, etc. Smash as a *tournament community* is less interested in that chaos part and more interested in those fighting game parts, plus pushing the limits of the game's control techniques.
My take is that items are part of the chaotic novelty, explicitly designed to help weaker players sometimes feel the thrill of victory (or to reduce the sting of losing; "it was just bad luck"). To me they seem about 80% on the axis toward "output randomness"--that is, one player is closest to the item as it spawns and is the only one with an opportunity to succeed with it. For some people and parties this is great! In fact, if you played enough matches then the randomness would eventually even out. But it's not a system where the randomness offers symmetric opportunities to both players, nor is it one where the randomness is forecasted in some way that allows players to really fight for an opportunity to use an item.* For the randomness to even out in a tournament, the event would probably need to do longer sets, and the power of items does distract from those interesting fundamentals of two players interacting that are at the core of the game.
This doesn't mean randomness is bad or that any game with randomness is not worthy of competitive pursuit! And I want to emphasize that Smash can still be very unpredictable even with the items and wacky stages disabled. I'm just trying to articulate why items are not the norm in the Smash tournament community. If you like the items, maybe you can find enough people who also prefer those rules and run your own smaller events!
* Well, I concede that items do always appear on the stage itself, so if you've launched an opponent off the stage then you might have a better chance to grab the item, but feel that it's fairly minor.